Generally, methods for detecting wetness events or liquid discharge to an absorbent article are known in the art. In a conventional system, a sensor monitors a resistance between two conductors arranged in a diaper and compares resistance values to a predetermined and fixed threshold resistance value. If the resistance value is less than the threshold resistance value, then the sensor sends a signal to an alarm device, which informs a caregiver and/or the wearer that the wearer has urinated.
A problem with such a system is that they may be prone to giving false positives, that is informing the caregiver and/or the user that there is urination present in the undergarment when there is not because there is only one “check” or “test” for the presence of micturition (i.e. whether the resistance of the undergarment falls below a fixed threshold value). Such false positives can depend on loose wiring, noise, or disturbances from unknown sources. Further, in certain situations, such as when the person wearing the diaper sits or if other pressure is applied to an undergarment that has been previously wetted, the resistance of the undergarment may fall below the threshold value, thus indicating a new micturition, when in fact a subsequent liquid discharge event has not occurred. Consequently, a false-positive will be detected.
Conventionally, the number of false positive detections is decreased by choosing a higher threshold value. However, a relatively high threshold value increases the risk of non-detection of small amounts of liquid discharge. Accordingly, conventional devices may be ill-suited for accurately detecting multiple micturitions and/or preventing the detection of false-positives. Moreover, sweat may at least somewhat saturate the undergarment, typically over a relatively lengthy period of time, and may trigger the sensor. Still moreover, after a first micturition by the wearer, the resistance value of the undergarment is substantially less than when the product was dry. However, the threshold value has not changed, and therefore, the resistance may be lower than the threshold, thus triggering an alarm, even though a subsequent liquid discharge event has not occurred.
For instance, WO 2008/075227 discloses a method of detecting the presence of a liquid discharge in an absorbent article. In general, a method according to one embodiment of WO 2008/075227 for detecting the presence of a liquid discharge within an absorbent article comprises: monitoring an electrical property of the article as the article is being worn by a wearer, wherein the electrical property changes in response to a liquid discharge; determining a slope in a parameter of the electrical property over time; and comparing the slope to a threshold value to determine the presence of liquid discharge. According to other embodiments of WO 2008/075227 the following can also be determined for detecting a liquid discharge: a comparison of the electrical property over a period of time to a threshold value; and/or a comparison of the electrical property to a determined threshold value.
However, there is still a need of improved methods that at least alleviates the problems of detection of false positives of prior art, allows for reliable detection of multiple micturitions, and is less sensitive for disorders, such as a short circuit of the conductors.